This invention relates to a magnetic marker for use in identification systems and particularly concerns a magnetic marker for reading identification information such as checkup data. The magnetic marker of the invention is applicable to electronic article surveillance systems, for prevention of forgery, as well as to data carriers and magnetic cards.
Article identify systems that use magnetic markers are known and a representative type is described in WO92/12402 with the title of invention of "Remotely Readable Data Storage Devices and Apparatus". This article identify system comprises a detection area for identification, an external alternating magnetic field producing means that is provided within the area and which performs sweeping through a range of frequencies to generate varying frequencies, a magnetic marker for use in identification systems as attached to an article that need be identified and that is predestined to pass through the area, the marker comprising an assembly of a magnetic layer that has been magnetized to have a magnetic pattern according to a bias magnetic field and a magnetostrictive metal (B) that will resonate mechanically at predetermined frequencies within the range of frequencies that are generated from the means within the area in such a way as to experience changes in magnetic flux density and permeability, the magnetic layer and the metal (B) being layered so that the latter is capable of mechanical resonance, the magnetic marker being so adapted that the predetermined frequencies at which the magnetic flux density or permeability changes is generated as an identification signal within the area according to the magnetic pattern provided in the magnetic layer by magnetization, and means for detecting the resonance of the marker at the predetermined frequencies which is generated from the means within the area. Thus, the identification system under consideration responds to the presence of the marker within the area.
According to page 11 of the specification of WO92/12402, an exemplary material that can be used is a plate that consists of a non-magnetic substrate having a magnetic coating thereon, such as slurry-formed ferrite as in magnetic tapes.
The conventional markers described above use the particles of magnetic materials such as ferrite and .gamma.-Fe.sub.2 O.sub.3, but the use of such magnetic powders suffers from a common defect in that the magnetic coating which constitutes the marker is fairly thick. The thick magnetic coating causes additional problems such as difficulty in manufacturing flexible markers and the increase in the number of production steps, which will lead to a lower productivity, occasionally to complete failure in manufacture.